Commit message: Fix bug #707 cert hostnames not being checked
- only happened when openssl v1.1 is used
CVE: CVE-2021-44273
CWE: CWE-295
Vulnerability description: e2guardian v5.4.x <= v5.4.3r is affected by missing SSL certificate validation in the SSL MITM engine. In standalone mode (i.e., acting as a proxy or a transparent proxy), with SSL MITM enabled, e2guardian, if built with OpenSSL v1.1.x, did not validate hostnames in certificates of the web servers that it connected to, and thus was itself vulnerable to MITM attacks.

Project: e2guardian
File: Socket.cpp

int Socket::startSslClient(const std::string &certificate_path, String hostname)
{
    if (isssl) {
        stopSsl();
    }

    ERR_clear_error();
#if OPENSSL_VERSION_NUMBER < 0x10100000L
    ctx = SSL_CTX_new(SSLv23_client_method());
#else
    ctx = SSL_CTX_new(TLS_client_method());
#endif

    if (ctx == NULL) {
#ifdef NETDEBUG
        std::cout << thread_id << "Error ssl context is null (check that openssl has been inited)" << std::endl;
#endif
        log_ssl_errors("Error ssl context is null for %s", hostname.c_str());
        return -1;
    }

    //set the timeout for the ssl session
    if (SSL_CTX_set_timeout(ctx, 130l) < 1) {
            SSL_CTX_free(ctx);
            ctx = NULL;
        return -1;
    }

    //load certs
    ERR_clear_error();
    if (certificate_path.length()) {
        if (!SSL_CTX_load_verify_locations(ctx, NULL, certificate_path.c_str())) {
#ifdef NETDEBUG
            std::cout << thread_id << "couldnt load certificates" << std::endl;
#endif
            log_ssl_errors("couldnt load certificates from %s", certificate_path.c_str());
            //tidy up
            SSL_CTX_free(ctx);
            ctx = NULL;
            return -2;
        }
    } else if (!SSL_CTX_set_default_verify_paths(ctx)) //use default if no certPpath given
    {
#ifdef NETDEBUG
        std::cout << thread_id << "couldnt load certificates" << std::endl;
#endif
            log_ssl_errors("couldnt load default certificates for %s", hostname.c_str());
        //tidy up
        SSL_CTX_free(ctx);
        ctx = NULL;
        return -2;
    }

    // add validation params
    ERR_clear_error();
    X509_VERIFY_PARAM *x509_param = X509_VERIFY_PARAM_new();
    if (!x509_param) {
        log_ssl_errors("couldnt add validation params for %s", hostname.c_str());
        //X509_VERIFY_PARAM_free(x509_param);
            SSL_CTX_free(ctx);
            ctx = NULL;
        return -2;
    }

    ERR_clear_error();
    if (!X509_VERIFY_PARAM_set_flags(x509_param, X509_V_FLAG_TRUSTED_FIRST)) {
        log_ssl_errors("couldnt add validation params for %s", hostname.c_str());
        X509_VERIFY_PARAM_free(x509_param);
            SSL_CTX_free(ctx);
            ctx = NULL;
        return -2;
    }

    ERR_clear_error();
    if (!SSL_CTX_set1_param(ctx, x509_param)) {
        log_ssl_errors("couldnt add validation params for %s", hostname.c_str());
        X509_VERIFY_PARAM_free(x509_param);
            SSL_CTX_free(ctx);
            ctx = NULL;
        return -2;
    }

    X509_VERIFY_PARAM_free(x509_param);     // try not freeing this as SSL_CTX_free seems to be ring to free it

    //hand socket over to ssl lib
    ERR_clear_error();
    ssl = SSL_new(ctx);
    SSL_set_options(ssl, SSL_OP_ALL);
    SSL_set_mode(ssl, SSL_MODE_AUTO_RETRY);
    SSL_set_connect_state(ssl);

    //fcntl(this->getFD() ,F_SETFL, O_NONBLOCK); // blocking mode used currently
    SSL_set_fd(ssl, this->getFD());
    SSL_set_tlsext_host_name(ssl, hostname.c_str());

    //make io non blocking as select wont tell us if we can do a read without blocking
    //BIO_set_nbio(SSL_get_rbio(ssl),1l);  // blocking mode used currently
    //BIO_set_nbio(SSL_get_wbio(ssl),1l); // blocking mode used currently
    ERR_clear_error();
    int rc = SSL_connect(ssl);
    if (rc < 0) {
        log_ssl_errors("ssl_connect failed to %s", hostname.c_str());
#ifdef NETDEBUG
        std::cout << thread_id << "ssl_connect failed with error " << SSL_get_error(ssl, rc) << std::endl;
#endif
        // tidy up
        SSL_free(ssl);
        ssl = NULL;
        SSL_CTX_free(ctx);
        ctx = NULL;
        return -3;
    }

    //should be safer to do this last as nothing will ever try to use a ssl socket that isnt fully setup
    isssl = true;
    issslserver = false;
    return 0;
}